1. Field of the Invention
The present invention relates to an apparatus for feeding a medium, such as paper, in a medium processing device such as a printer. More particularly, the present invention relates to an improved apparatus for increasing the precision in a feed operation of the medium through the medium processing device.
2. Background Art
As is disclosed in U.S. Pat. No. 5,088,848 (assigned to Olivetti), shown in FIG. 5, the correction of position of an inserted medium is made by running the edges of the medium against a left guide 171, and shutters 121, 123, 125 and 127. Then the medium is fed into the processing device, such as a printer. FIG. 5 is a plan view of a portion of the medium processing device 100 parallel to a feed path.
In this approach, the medium 200 is inserted, and when an IN sensor (an insertion sensor) 163 is turned on, rotation of an align roller 151 arranged in a lateral direction and align rollers 141 and 143 arranged in a vertical direction is initiated.
The align roller 151 feeds the medium in a leftward direction, and the align rollers 141 and 143 feed the medium in a forward direction. The shape of these two kinds of rollers is oval rather than circular, as shown in cross section A—A and cross section B—B. These rollers contact with idlers 145 and 153, respectively, for each rotation of 180 degrees. The idlers 145 and 153 are applied with a bias force such as a spring in a direction toward the align rollers so that a proper feed force or a feed power (a force for sustaining the feed operation) is generated.
The top of the align roller 151 is shifted from the tops of the align rollers 141 and 143 by 190 degrees, as shown in FIGS. 5, to alternately feed the medium incrementally toward the leftward direction and then in the forward direction. That is, when one, such as the align roller 151, feeds, the medium, the other, such as align rollers 141 and 143, does not disturb the feed operation of the align roller 151. When align sensor 165 is turned off, align roller 151 is operated, and when align sensor 165 is turned on, align roller 151 is stopped. When sensor 161 is turned off, align rollers 141 and 143 are operated, and when align sensor 161 is turned on, align rollers 141 and 143 are stopped. Finally, medium 200 is stopped by the left guide 171 and shutters 121, 123, 125 and 127.
As shown in FIG. 7, when both align sensors 161 and 165 are turned on, the correction of position is considered to be completed, and align rollers 141, 143 and 151 are stopped. Then the shutters 121, 123, 125 and 127 are opened, and the medium is fed into the inside of the processing device by feed rollers 131 and 133, and a process, such as a print operation or a character recognition operation, is performed.
However, when the medium is very thin, or the surface of the medium is very smooth, a sufficient friction force between a back surface of the medium and a surface of a plate for supporting the medium is not generated. Accordingly, when the oval shaped align rollers 141, 143, and 151 do not contact the idlers 145 and 153, the inertia force of the medium 200 driven by the previous contact with the align rollers 141, 143 and 151 becomes larger than the friction force of the surface of the medium, so that an overrun of the medium 200 occurs. As a result, when the medium 200 runs against the left guide 171 or the shutters 121, 123, 125 and 127, a bounce back of the medium 200 occurs, so that a proper correction of position of the medium becomes impossible.
One approach to solve this problem is to decrease the inertia force of the medium to the same strength as the friction force of the medium by either decreasing the rotational speed of the align rollers 141, 143 and 151 or by using align rollers with a smaller diameter so as to decrease the amount of movement of the medium. This alternative approach, however, increases the time for processing the medium to an unacceptable level.
Accordingly, one object of the present invention is to provide a mechanism for feeding a medium at a high speed which is not affected by a physical characteristic, such as thinness or smoothness, of the medium.
Another object of the present invention is to provide a mechanism for realizing a high speed correction of position of the medium which is not affected by a physical characteristic of the medium.
Still another object of the present invention is to provide a feed mechanism for decreasing a shear force or a tension force applied to the medium to as small a value as possible.
Another object of the present invention is to provide an improved feed mechanism in which production cost is low and the number of fabrication steps are decreased to a minimum.